1. Field
Example embodiments relate to vertical light-emitting devices wherein an emitting unit is patterned to form a pattern array.
2. Description of the Related Art
Nitride semiconductor-based light-emitting devices are classified into horizontal light-emitting devices and vertical light-emitting devices. Unlike the horizontal light-emitting devices, wherein a part of a semiconductor layer is etched and an electrode is formed on the etched part of the semiconductor layer, the vertical light-emitting devices include electrodes that are directly disposed on top and bottom surfaces of a semiconductor structure, and thus a current may be efficiently applied from the electrodes to the semiconductor structure. Accordingly, the vertical light-emitting devices have improved efficiency and an improved output, compared to the horizontal light-emitting devices.
The nitride semiconductor-based light-emitting devices include an epitaxial nitride semiconductor layer grown on a sapphire substrate by using, for example, a metal-organic chemical vapor deposition (MOCVD) method. However, the sapphire substrate is relatively expensive, and it is difficult to use a large size sapphire substrate in a vertical device due to an insulating property of the sapphire substrate.
A silicon substrate, which is widely used in the semiconductor industry, is inexpensive and a large dimension substrate may be obtained with relative ease. Thus, methods of growing a nitride semiconductor by using the silicon substrate are being conducted in fields of fabricating a nitride semiconductor.
An epitaxial growth according to the MOCVD method is performed at a high temperature of about 1000° C. or above, and differences of lattice constants and thermal expansion coefficients between a substrate and a nitride semiconductor are considered when selecting the substrate. The difference of the lattice constants may increase dislocation density, and the difference of the thermal expansion coefficients may cause substrate bending while cooling the substrate to room temperature. Since silicon has a larger thermal expansion coefficient than gallium nitride (GaN), a tensile stress may be applied to a GaN layer, thereby cracking a nitride semiconductor. Such cracks may worsen as the size of the substrate is increased. Accordingly, it is important to reduce the generation of the cracks while growing the nitride semiconductor using the silicon substrate.